The invention relates to a method for detecting signal errors, in particular for detecting rpm signal errors, in order to detect missing signals and to distinguish those errors from changes in rpm. Distinguishing missing signals from rpm changes is significant if unintentional tripping, or tripping that is not authorized by the existing driving situation of a motor vehicle, of antilock and traction control systems in motor vehicles are to be prevented.
European Patent Disclosure EP 0 193 335 B1 discloses a device for detecting an anomaly in a rotary speed sensor. This sensor is used to detect a rotary speed of a rotating body. An electronic device is provided which responds to a signal of the rotary speed sensor in order to measure an interval between successive signals. Devices are also provided for estimating a time period, from the previously measured time interval; within the time period, a subsequent signal is generated by the rotary speed sensor. Devices are also known that detect an anomaly of the rotary speed sensor if the signal is not generated within the estimated period of time. In this method, the estimation of a new period of time is done by adding a fixed time difference to the applicable preceding period of time. Because of the estimate that must be made, the method proposed in EP 0 193 335 B1 is subject to imprecision.
In technical applications, such as automobile manufacture, active sensors are increasingly used at present. When such sensors are used, gear wheels are increasingly being replaced by magnet rings (multipoles). In maintenance work or at repair facilities, these magnet rings can be damaged by incorrect manipulation, for example, or impaired by magnetic dirt sticking to them. The dirt adhering to the magnet rings, like damage to the magnet rings, can lead to missing signals. This can mean that entire pole segments are blanked out, which in antilock or traction control systems can mean that the system will respond to the absence of rpm pulses even though no critical driving situation exists, yet the ABS or TCS does perform control functions.
With the method proposed according to the invention, rpm changes can be very easily distinguished from errors without requiring the presence of a reference signal. There is no need for the wheel or wheels whose rpm is to be scanned to be moved into specified circumferential positions, for the method proposed by the invention to be usable. The proposed method can be realized in software form or by means of hardware components; the expense for hardware components is considered low. The test conditions to be performed independently of one another make reliable detection of phases of speed change impossible, that is, acceleration and deceleration, so that these phases can be distinguished from incident errors. The test routine with two comparisons independent from one another can be performed over a plurality of wheel revolutions, making a simply designed filtering feasible. With the method proposed according to the invention, the absence of individual poles and/or of entire pole segments can easily be detected.
An assessment of each individual wheel of the motor vehicle is possible independently of the other wheels, and so scattering per wheel can very easily be distinguished from genuine signal errors.